Method of fracturing using ultra lightweight proppant suspensions and gaseous streams

ABSTRACT

In a method of hydraulically fracturing a hydrocarbon-bearing subterranean formation, a proppant stage is introduced into the fracture which contains a gaseous fluid and an ultra lightweight proppant suspended in a viscosified aqueous fluid. The gaseous fluid of the proppant stage contains at least about 90 volume percent of the combination of gaseous fluid and aqueous fluid. A pad fluid may first be introduced into the formation, the pad fluid containing a gaseous fluid and, optionally, an aqueous fluid. The gaseous fluid of the pad fluid mixture typically contains at least 70 volume percent of the mixture.

FIELD OF THE INVENTION

The invention relates to a method of hydraulic fracturing a subterraneanformation by introducing into the formation a proppant stage containinga gaseous fluid and an ultra lightweight (ULW) proppant suspended in aviscosified or gelled aqueous fluid.

BACKGROUND OF THE INVENTION

A common method of increasing productivity of a hydrocarbon-bearingformation penetrated by a wellbore is to subject the formation tostimulation techniques, such as hydraulic fracturing. In hydraulicfracturing, a liquid, gas or two-phase fluid, generally referred to as afracturing fluid, is introduced into the formation. The fracturingfluid, typically water or oil-based, is introduced into the wellborepenetrating the formation at a sufficient pressure and flow rate tocreate fractures in the subterranean formation. A proppant is introducedinto the fractures to keep the fractures open. The propped fractureprovides larger flow channels through which an increased quantity of ahydrocarbon may flow, thereby increasing the productive capability ofthe well.

Recently, ultra lightweight (ULW) particulates have been reported foruse as proppants. The requisite fluid velocity to maintain proppanttransport within the fracture is reduced by the use of ULW proppants. Inlight of reduced fluid velocity, a greater amount of the createdfracture area may be propped. Exemplary of such ULW proppants are thoseset forth in U.S. Patent Publication No 2008/0087429 A1, hereinincorporated by reference.

Many times, fracturing proceeds by first introducing into the formationa “pad” or “spearhead” fluid. Pad or spearhead fluids are fracturingfluids used to initiate fractures and are typically free of proppant.They normally exhibit relatively low viscosity. Following the initiationof the fracture, fracturing fluid containing proppant is then introducedinto the formation.

Fracturing fluids which are predominately liquid typically exhibit poortransport properties. High pumping rates are normally required in orderto impart a sufficient velocity for placement of the proppant in thefracture. In such treatments, the proppant tends to settle, forming a‘proppant bank’, as the linear slurry velocity falls as a function ofthe distance from the wellbore. This effect is further believed toresult in reduced stimulation efficiency as the effective propped lengthis relatively short.

Further complications arise from the use of liquid fracturing fluidsbecause of the need to recover the fracturing fluid. Such fracturingfluids typically contain components which are damaging to theenvironment and/or affect the production of oil and/or gas from thereservoir. For instance, water soluble polymers, such as guar gum or aderivative thereof, are often used in fracturing fluids to provide therequisite flow characteristics to the fluid and to suspend proppantparticulates. When pressure on the fracturing fluid is released and thefracture closes around the proppant, water is forced out and thewater-soluble polymer forms a filter cake. This filter cake can preventoil or gas flow if it is not removed. Further, emulsions may begenerated from fracturing fluids which impede flow of produced gasand/or oil.

The recovery of fracturing fluids and the removal of filter cakes isnormally accomplished by reducing the viscosity of the fluid with abreaker such that the fracturing fluid flows naturally from theformation under the influence of hydrostatic pressure. Historically, theapplication of breakers in fracturing fluids at elevated temperatures,i.e., above about 120-130° F., has been a compromise between maintainingproppant transport and achieving the desired fracture conductivity,measured in terms of effective propped fracture length. Conventionaloxidative breakers react rapidly at elevated temperatures, potentiallyleading to catastrophic loss of proppant transport. Encapsulatedoxidative breakers have experienced limited utility at elevatedtemperatures due to a tendency to release prematurely or to have beenrendered ineffective through payload self-degradation prior to release.

Alternative fracturing treatments have been explored by incorporatinggaseous materials into fracturing fluids in order to form a gas phase atthe wellhead or at the formation being fractured or both. In “foamfracturing”, a foam is generated of a desired Mitchell quality which isthen introduced through the wellbore into the formation. For instance,U.S. Pat. No. 3,937,283 discloses a hydraulic fracturing processemploying a foam formed of a gas (such as nitrogen, carbon dioxide, airor a hydrocarbon gas) and a liquid (such as water or an oil baseliquid). The foam is characterized as having a Mitchell quality withinthe range of 52.4% to 99.99% and preferably between the range of 60% to85%. The pressure at which the foam is pumped into the well is such thata fracture of the hydrocarbon-bearing formation is created. The foameasily exits the well when pressure is released from the wellhead. Thereduction in pressure causes the foam to expand.

Conventional fracturing operations, including those wherein a gaseousmaterial is incorporated into the fracturing fluid, have been found tobe inappropriate for the creation of partial monolayer fractures.Partial monolayer fractures are created by a proppant pack havingproppant particulates widely spaced from each other, the proppant packexhibiting the requisite strength to hold fractures open and thus allowthe production of hydrocarbons from the formation.

The efficiency of a partial monolayer fracture is dependent on fractureporosity and conductivity once the fracturing operation is stopped andproduction commences. Fracture porosity is dependent upon the areaconcentration of the proppant placed, the proppant size, and mechanicalproperties, e.g, modulus, of the proppant. It is important that proppantpacks forming partial monolayer fractures exhibit high porosity. Thehigh conductivity of the created fractures is attributable to theability of produced fluids to flow around the widely spaced proppantparticulates instead of being confined to the relatively smallinterstitial spaces evidenced in the packed proppant bed.

Alternative hydraulic fracturing methodologies have been sought whichprovide increased conductive fracture areas and increased effectivepropped fracture lengths. Such alternative methodologies need to renderimproved stimulation efficiency and well productivity and provide ameans to create partial monolayer fractures. In addition, suchmethodologies need to minimize or eliminate the reservoir damageevidenced from the use of liquid fracturing fluids.

SUMMARY OF THE INVENTION

The invention relates to a method of hydraulically fracturing ahydrocarbon-bearing subterranean formation by introducing into thefracture at least one proppant stage which contains a gaseous fluid andan ultra lightweight (ULW) proppant suspended in a viscosified orsurfactant gelled aqueous fluid. The gaseous fluid of the proppant stagecontains at least about 85 volume percent of the combination of gaseousfluid and aqueous fluid. The ULW proppant has an apparent specificgravity less than or equal to 2.45.

The ULW proppant is suspended in the viscosified or surfactant gelledaqueous fluid prior to being admixed with the gaseous fluid. The amountof proppant suspended in the surfactant gelled aqueous system orviscosified aqueous fluid is that amount sufficient to create a partialmonolayer in the fracture.

The pumping of the proppant stage may be preceded by introduction of apad fluid. The pad fluid contains a gaseous fluid and is introduced intothe formation at a pressure sufficient to initiate a fracture. The padfluid may further contain an aqueous fluid. Typically, the gaseous fluidof the pad fluid mixture comprises at least 70 volume percent of the padfluid mixture. The pad fluid may further contain a proppant, preferablyan ULW proppant having an apparent specific gravity less than or equalto 2.25.

The disclosed methodology improves proppant placement and conductivefracture area, while minimizing fracture conductivity damage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fracturing method described herein consists of introducing into thefracture within a formation a proppant stage containing a gaseous fluidand a viscosified aqueous fluid in which the proppant is suspended. Theproppant stage is created by the mixing of the gaseous fluid and theviscosified aqueous fluid containing suspended proppant at the wellhead.

The amount of gaseous fluid contained in the proppant stage fluid is atleast about 85 volume percent, i.e., the combination of gaseous fluidand aqueous fluid, which contains the proppant, is at least about 85volume percent. Typically, the amount of gaseous fluid in the proppantstage fluid is greater than or equal to 90 volume percent. Usually, atleast about 95 percent of the proppant particulates in the proppantstage are not in contact with other proppant particulates in the createdfracture.

The described method of fracturing creates a large conductive fracturearea in the formation with a minimal amount of liquid fluid. The proppedfracture area exhibits high conductivity using a minimal volume ofliquid fluid in the proppant stage. As a result, there is minimal, ifany, damage to conductivity. Since the proppant stage is composedpredominately of gas, the amount fracturing fluid that must be recoveredis minimal. Further, damage to the reservoir, often affiliated with theuse of liquid fracturing fluids, is minimized or eliminated. Forinstance, since the amount of liquid in the proppant stage fluid isminimized, damage caused by polymers, emulsions and water blocks whichroutinely results with liquid fracturing fluids is dramatically reduced,if not eliminated. Environmental impact from the fracturing methoddisclosed herein is thereby reduced.

The disclosed methodology further provides easier movement of reservoirfluids (gas and/or oil), especially in low pressure or under-pressuredreservoirs. When liquid fracturing fluids are employed, the liquidcolumn in the casing and wellbore imparts a hydrostatic pressure on thereservoir, necessitating that the reservoir has sufficient greaterpressure than the applied hydrostatic pressure to push the fracturingfluid out of the wellbore. In light of the low amount of liquid used inthe inventive fracturing fluid, the amount of hydrostatic pressure to beovercome, if any, to allow flow of oil or gas out of the reservoir isminimized or eliminated. In addition, since the disclosed methodologyuses less liquid and proppant in the fracturing fluid than conventionalfracturing processes, equipment demands are decreased and operationalcosts are reduced.

Further, the method of fracturing a hydrocarbon-bearing subterraneanformation, as defined by the invention, is capable of creating a partialmonolayer of proppant in the fracture upon closure of the fracture.Properly placed, the partial monolayer provides the most efficientconductivity for the amount of proppant employed. The partial monolayeris created by the use of a small amount of aqueous fluid in the proppantstage; the fluid in the proppant stage being mostly an inert gas, suchas nitrogen. Proppants in partial monolayers further are generally lesssusceptible to flowback in light of their improved confinement. Further,produced fluids flowing through a partial monolayer have a reducedtendency of proppant flowback during production of oil and/or gas fromthe well. Fluid recovery after treatment is thereby greatly enhanced forhigh well productivity.

In the method defined herein, a ULW proppant is first slurried in anaqueous fluid. A slurry concentrate is preferred since it makes theoperational procedure more logistically acceptable as a greater amountof proppant per given volume is made available on-site and in thevicinity of the blender/mixer. The ULW proppant is then suspended in aviscosified aqueous fluid prior to being admixed with the gaseous fluid.To do so, the ULW proppant slurry was introduced to the viscosifiedfluid at a temperature of less than 100° F. and agitated for about 30minutes.

The amount of proppant suspended in the viscosified aqueous fluid isthat amount sufficient to create a partial monolayer in the fracture.Prior to being suspended in the viscosfied aqueous fluid, theconcentration of ULW proppant in the aqueous fluid is normally betweenfrom about 2 to about 8 pounds per gallon of liquid (ppa).

The slurry, containing the ULW proppant, is introduced into a blender ormixer and a viscosifying agent is then added. The admixture is stirreduntil the proppant becomes suspended in the aqueous fluid. Vigorousagitation may be required to prevent gravity segregation of the proppantwhile the viscosifying agent is being introduced. The suspension may bebatch-mixed or made on-the-fly. At least one high pressure pump is usedto inject the proppant slurry into the wellhead.

The viscosifying agent may be a synthetic or natural polymer.

In a preferred embodiment, the viscosifying agent is a viscoelasticsurfactant. Upon agitation, the ULW proppant becomes suspended in theviscoelastic surfactant as the viscoelastic surfactant commencesgelation.

The amount of viscosifying agent added to the aqueous fluid containingthe proppant is that amount sufficient to suspend the proppant in theresulting medium. Typically, the amount of viscosifying agent added tothe aqueous fluid is from about 1 to about 15 gallons per thousand (gpt)of aqueous fluid.

Typically, the weight percent of proppant in the suspension is betweenfrom about 6 to about 55 weight percent, preferably between from about19 to about 49 weight percent. Further, the requisite amount of proppantmay be adjusted by varying the rate of gas introduced into the operationmixer/blender with the aqueous fluid or by varying the rate of proppantslurry into the mixer/blender. Typical downhole proppant concentrationsare approximately 0.05 per gallon (ppg) of fluid in the proppant stage(including the gaseous phase) at downhole conditions of pressure andtemperature and may increase to 0.5 ppg. The low concentration ofproppant facilitates the ability to attain a very dispersed proppantdistribution upon fracture closure and thus to obtain the desiredpartial monolayer. The injection rate of proppant slurry into thewellhead may be adjusted to obtain the desire downhole proppantconcentration.

The fluid containing the suspended proppant is added to the gaseousstream. Typically, the gaseous stream is introduced directly at thewellhead and is concurrently admixed with the aqueous proppantsuspension at the wellhead.

Suitable synthetic or natural polymers are those hydratable polymerswhich contain one or more functional groups, such as a hydroxyl,carboxyl, sulfate, sulfonate, amino or amido group. Preferred syntheticand natural polymers include polysaccharides, polyvinyl alcohols,polyacrylates (including the (meth)acrylates), polypyrrolidones,polyacrylamides (including (meth)acrylamides) as well as2-acrylamido-2-methylpropane sulfonate and mixtures thereof.

Other suitable polysaccharides and derivatives are those which containone or more monosaccharide units of galactose, fructose, mannose,glucoside, glucose, xylose, arabinose, glucuronic acid and pyranosylsulfate. These include guar gums and derivatives thereof, locust beangum, tara, xanthan, succinoglycan, scleroglucan and carrageenan.

Preferred viscosifying polymers may include crosslinkablepolysaccharides, such as guar gums and derivatives, cellulose, starch,and galactomannan gums. Cellulose and cellulose derivatives includealkylcellulose, hydroxyalkyl cellulose or alkylhydroxyalkyl cellulose,carboxyalkyl cellulose derivatives such as methyl cellulose,hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose,hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose,hydroxybutylmethyl cellulose, methylhydroxyethyl cellulose,methylhydroxypropyl cellulose, ethylhydroxyethyl cellulose,carboxyethylcellulose, carboxymethylcellulose andcarboxymethylhydroxyethyl cellulose.

Specific examples of polysaccharides useful with the present inventioninclude, but are not limited to, guar gum, hydroxypropyl guar,carboxymethylhydroxypropyl guar and known derivatives of these gums.

Suitable surfactant based gels for use in practicing the invention maybe prepared from viscoelastic surfactants containing an anionicsurfactant and a cationic surfactant. A preferred viscoelasticsurfactant is the combination of sodium xylene sulfonate, as anionicsurfactant, and N,N,N-trimethyl-1-octadecammonium chloride, as cationicsurfactant. Such viscoelastic surfactants are set forth in U.S. Pat. No.6,468,945, herein incorporated by reference. The volume ratio of anionicsurfactant:cationic surfactant is from about 1:4 to about 4:1.

Other suitable surfactant based gelled systems are those fluids whichcontain a C₁₀ to C₂₄ alkyl trialkyl quaternary ammonium aromatic saltadmixed with an anionic surfactant, such as sodium xylene sulfonate.Such systems include those set forth in U.S. Patent Publication No.20040138071, herein incorporated by reference. Typically, the volumeratio of cationic surfactant:anionic surfactant of such viscoelasticsurfactants is between from about 1:1 to about 3:1. The alkyl groupforming the alkylated moiety can be a C₁₀ to C₂₄ alkyl group, preferablya C₁₂ to a C₂₀ alkyl. In a most preferred embodiment, the alkyl groupforming the alkylated moiety is a C₁₈ alkyl. The aromatic salt ispreferably an aromatic salicylate or phthalate. The trialkyl moietycontains preferably from C₁ to C₄ alkyl groups, most preferably methyl.In a preferred mode, the surfactant is a gelled C₁₈ trimethyl quaternaryammonium phthalate or a gelled C₁₈ trimethyl quaternary ammoniumsalicylate.

Such C₁₀ to C₂₄ alkyl trialkyl quaternary ammonium aromatic salts may beformed by mixing a C₁₀ to C₂₄, preferably a C₁₈, alkyl trialkylquaternary ammonium chloride with an alkali aromatic salt, such as asodium salt of either salicylic acid or phthalic acid.

The ULW proppant has an apparent specific gravity (ASG) less than orequal to 2.45, generally is less than or equal to 2.25, typically lessthan or equal to 2.0, preferably less than or equal to 1.75, morepreferably less than or equal to 1.25, most preferably less than orequal to 1.06. Such ULW proppants more easily facilitate the placementof partial monolayers within the formation.

Exemplary ULW proppants for use in the invention include naturallyoccurring material resistant to deformation, a synthetic polymericparticulate, a porous particulate treated with a non-porous penetratingcoating and/or glazing material or a well treating aggregate of anorganic lightweight material and a weight modifying agent. Such ULWproppants are disclosed in U.S. Patent Publication No 2008/0087429 A1,herein incorporated by reference.

Further, the ULW proppant may be a polyamide, such as those disclosed inUS-2007-0209795 A1, herein incorporated by reference.

Further, the ULW proppant may be metallic spheres, such as thosedisclosed in U.S. patent application Ser. No. 12/018,050 on Jan. 22,2008.

The ULW proppant may be any of those deformable particulates set forthin U.S. patent application Ser. No. 12/019,723, filed on Jan. 25, 2008and U.S. Pat. No. 7,322,411, both of which are herein incorporated byreference.

Still preferred are synthetic polymers, such as polystyrene beadscrosslinked with divinylbenzene. Such beads include those described inU.S. Patent Publication No. 2007 0209794 A1, herein incorporated byreference.

Mixtures of proppants may further be used.

The gaseous fluid to which the viscosified aqueous fluid containing thesuspended proppant is added is preferably either an inert gas, such asnitrogen, carbon dioxide, air, natural gas or a combination thereof.Nitrogen is most preferred. The gaseous fluid comprises at least about90 volume percent of the fluid in the proppant stage.

A pad fluid may precede the introduction of the proppant stage into theformation. The pad fluid is a gaseous fluid and is introduced into theformation at a pressure sufficient to initiate a fracture. The pad fluidis preferably composed entirely of nitrogen or a mixture of nitrogen.The pad fluid may further contain an aqueous fluid, including theviscosified fluid (with or without proppant) set forth above. Where thepad fluid contains a mixture of gaseous fluid and aqueous fluid, theamount of gaseous fluid in the pad fluid mixture is at least 70,preferably at least 90, more preferably at least 95, volume percent. Thepad fluid may further contain one or more proppants. Typically, whenpresent, the ASG of the proppant in the pad fluid is less than the ASGof the proppant present in the proppant stage. In a preferredembodiment, the ASG of the proppant in the pad fluid is less than orequal to 2.25.

The following example is illustrative of some of the embodiments of thepresent invention. Other embodiments within the scope of the claimsherein will be apparent to one skilled in the art from consideration ofthe description set forth herein. It is intended that the specification,together with the examples, be considered exemplary only, with the scopeand spirit of the invention being indicated by the claims which follow.

EXAMPLE

A fracturing treatment was proposed for a Niobrara Chalk formationhaving a depth to middle perforation of 1,034 ft; a bottom hole statictemperature of approximately 73° F., a bottom hole fracture pressure ofapproximately 724 psi; a surface treating pressure (max) ofapproximately 751 psi; and a fracture gradient of about 0.70 psi/ft. Thedesired result was a partial monolayer distribution of proppant uponfracture closure. It was determined that the fracturing treatment wouldrequire approximately 10,000 pounds of ultra lightweight proppant. TheULW proppant selected was LiteProp™ 108, a thermoplastic ultralightweight proppant of 14/40 mesh, having an apparent specific gravityof about 1.05, a product of BJ Services Company. The estimated liquidproppant concentration was estimated to be approximately 4 pounds ofproppant added per gallon of liquid (ppa). This represents the estimatedconcentration of proppant needed to accommodate the flow rates of thepumps. Further, the mass of proppant per volume of viscosified liquidfluid was estimated to be 2.77 ppg, the total amount of fluid requiredfor treatment was estimated to be 2500 gallons and the density ofviscosified aqueous fluid containing proppant was estimated to be 8.55lbs/gal.

LiteProp™ 108 was suspended on-site in an aqueous carrier in a mixingunit, the apparent specific gravity ratio of proppant:carrier beingabout 1.08:1.00, to render a liquid concentration of 4 ppa. Aviscosifier was then added to the mixing unit while agitating theslurry. The viscosifier and amount added to the slurry was C₁₈ trimethylquaternary ammonium chloride [3.5 gallons per thousand (gpt) and 50/50blend of C₁₈ trimethyl quaternary ammonium chloride and sodium xylenesulfonate (10.0 gpt). The resultant was proppant suspended in theviscosified aqueous fluid. The proppant suspension was then pumped intothe formation while nitrogen was pumped into the wellhead.

Six treatment stages were undertaken at a rate of 25 barrels per minute(bpm). In the first treatment stage, a pad fluid of nitrogen gas andbetween from about 3 to about 5 gpt of the 50/50 blend of C₁₈ trimethylquaternary ammonium chloride and sodium xylene sulfonate was introducedinto the formation. In the stages 2-5, the viscosified proppantsuspension was admixed with nitrogen gas at the wellhead, as set forthabove. The last treatment stage was a nitrogen flush which did notcontain any proppant or surfactant. The parameters of the stages, basedon downhole temperatures and pressures, are set forth below in Table I:

TABLE I Downhole Proppant Proppant Prop. Vol. Mitchell Proppant FluidRate Cum. Quality*, Volume Conc. Rate Dry Liquid Dry Liquid calc., Stage(gal) (ppa) (bpm) (ppm) (gpm) (lbs) (gal) downhole, % 1 13,500 0 1.3 0.00.0 0 0 95.00 2 6,000 0.1 0.89 103.8 37.5 600 217 98.00 3 10,000 0.21.77 205.4 74.2 2,600 939 97.00 4 10,000 0.3 2.62 304.9 110.1 5,600 202295.00 5 11,000 0.4 3.45 402.2 145.2 10,000 3610 93.00 6 672 0 0 0.0 0.010,000 2,777 100.00 *Volume of gas/(volume gas + gel); does not includeproppant concentration.The proppant fluid approximates the number of pounds of proppantrequired to effectuate the desired downhole concentration of proppant.From the dry rate, the effective liquid rate is determined based on theamount of fluid added.

The treatment set forth rendered a partial monolayer distribution ofproppant in the fractures upon closure.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the true spirit andscope of the novel concepts of the invention.

1. A method of fracturing a subterranean formation comprisingintroducing a proppant stage into the subterranean formation fracture,wherein the proppant stage comprises a gaseous fluid and an ultralightweight (ULW) proppant suspended in a viscosified aqueous fluid andfurther wherein the gaseous fluid constitutes at least about 85 volumepercent of the combination of gaseous fluid and aqueous fluid in theproppant stage.
 2. The method of claim 1, wherein at least 90 percent ofthe proppant particulates in the proppant stage are not in contact withother proppant particulates.
 3. The method of claim 2, wherein at least95 percent of the proppant particulates in the proppant stage are not incontact with other proppant particulates.
 4. The method of claim 1,wherein the gaseous fluid is nitrogen, carbon dioxide or a combinationthereof.
 5. The method of claim 1, wherein the apparent specific gravityof the ULW proppant is less than or equal to 2.25.
 6. The method ofclaim 5, wherein the apparent specific gravity of the ULW proppant isless than or equal to 1.25.
 7. The method of claim 6, wherein theapparent specific gravity of the ULW proppant is less than or equal to1.06.
 8. The method of claim 1, wherein the viscosified aqueous fluidcontains a viscosifying agent selected from the group consisting ofpolysaccharides, polyvinyl alcohols, polyacrylates, polypyrrolidones andpolyacrylamides and mixtures thereof.
 9. The method of claim 8, whereinthe viscosifying agent is a polysaccharide, optionally crosslinked,selected from the group consisting of guar gums, guar derivatives,cellulose, starch, and galactomannan gums.
 10. The method of claim 1,wherein the viscosified aqueous fluid contains at least one viscoelasticsurfactant.
 11. The method of claim 1, wherein the viscosified aqueousfluid contains, as a viscosifying agent, the combination of at least oneanionic surfactant and at least one cationic surfactant.
 12. The methodof claim 11, wherein the anionic surfactant is sodium xylene sulfonateand the cationic surfactant is N,N,N-trimethyl-1-octadecammoniumchloride.
 13. A method of fracturing a subterranean formationcomprising: pumping a pad fluid comprising a gaseous fluid into theformation at a pressure sufficient to initiate a fracture; introducing aproppant stage into the fracture, wherein the proppant stage comprisesgaseous fluid and an ultra lightweight (ULW) proppant suspended in asurfactant gelled aqueous system and further wherein the gaseous fluidcomprises at least about 90 volume percent of the fluid in the proppantstage.
 14. The method of claim 13, wherein the pad fluid comprises agaseous fluid and an aqueous fluid.
 15. The method of claim 14, whereinthe pad fluid comprises a mixture of gaseous fluid and viscosifiedaqueous fluid, wherein the gaseous fluid of the pad fluid mixturecomprises at least 70 volume percent of the mixture.
 16. The method ofclaim 15, wherein the gaseous fluid of the pad fluid mixture comprisesat least 90 volume percent of the mixture.
 17. The method of claim 16,wherein the pad fluid further contains a proppant.
 18. The method ofclaim 17, wherein the proppant in the pad fluid has an apparent specificgravity less than or equal to 2.25.
 19. A method of fracturing asubterranean formation comprising: pumping a pad fluid comprising agaseous fluid into the formation at a pressure sufficient to initiate afracture; and introducing a proppant stage into the fracture, whereinthe proppant stage comprises gaseous fluid and an ultra lightweight(ULW) proppant suspended in a viscosified aqueous system and furtherwherein the gaseous fluid of the proppant stage comprises at least about90 volume percent of the fluid in the proppant stage.
 20. The method ofclaim 19, wherein the pad fluid comprises a gaseous fluid and an aqueousfluid.
 21. The method of claim 20, wherein the pad fluid comprises amixture of gaseous fluid and viscosified aqueous fluid, wherein thegaseous fluid of the pad fluid comprises at least 70 volume percent ofthe mixture.
 22. The method of claim 21, wherein the gaseous fluid ofthe pad fluid mixture comprises at least 90 volume percent of themixture.
 23. The method of claim 22, wherein the pad fluid furthercontains a proppant.
 24. The method of claim 23, wherein the proppant inthe pad fluid has an apparent specific gravity less than or equal to2.25.
 25. A method of fracturing a subterranean formation comprising:pumping a pad fluid comprising a gaseous fluid into the formation at apressure sufficient to initiate a fracture; and introducing a proppantstage into the fracture, wherein the proppant stage comprises gaseousfluid and an ultra lightweight (ULW) proppant suspended in aqueous brinehaving a specific gravity of near neutral buoyancy with the proppant,and further wherein the gaseous fluid comprises at least about 90 volumepercent of the fluid in the proppant stage.
 26. The method of claim 25,wherein the pad fluid comprises a gaseous fluid and an aqueous fluid.27. The method of claim 25, wherein the pad fluid comprises a mixture ofgaseous fluid and viscosified aqueous fluid, wherein the gaseous fluidof the pad fluid comprises at least 70 volume percent of the mixture.28. The method of claim 27, wherein the gaseous fluid of the pad fluidmixture comprises at least 90 volume percent of the mixture.
 29. Themethod of claim 25, wherein the pad fluid further contains a proppant.30. The method of claim 29, wherein the proppant in the pad fluid has anapparent specific gravity less than or equal to 2.25.
 31. A method offracturing a subterranean formation comprising pumping into theformation a proppant stage, wherein the proppant stage comprises gaseousfluid and an ultra lightweight (ULW) proppant suspended in a surfactantgelled aqueous system and further wherein the gaseous fluid comprises atleast about 85 volume percent of the fluid in the proppant stage, theamount of proppant suspended in the surfactant gelled aqueous systembeing that amount sufficient to create a partial monolayer in thefracture.
 32. The method of claim 31, wherein gaseous fluid comprises atleast 90 volume percent of the fluid in the proppant stage.
 33. Themethod of claim 31, wherein the apparent specific gravity of the ULWproppant is less than or equal to 2.25.
 34. The method of claim 33,wherein the apparent specific gravity of the ULW proppant is less thanor equal to 1.25.
 35. The method of claim 34 wherein the apparentspecific gravity of the ULW proppant is less than or equal to 1.06. 36.A method of fracturing a subterranean formation comprising pumping intothe formation a proppant stage, wherein the proppant stage comprisesgaseous fluid and an ultra lightweight (ULW) proppant suspended in aviscosified aqueous system and further wherein the gaseous fluidcomprises at least about 90 volume percent of the fluid in the proppantstage, the amount of proppant suspended in the viscosified aqueoussystem being that amount sufficient to create a partial monolayer in thefracture.
 37. The method of claim 36, wherein the apparent specificgravity of the ULW proppant is less than or equal to 2.25.
 38. Themethod of claim 37, wherein the apparent specific gravity of the ULWproppant is less than or equal to 1.25.
 39. The method of claim 38,wherein the apparent specific gravity of the ULW proppant is less thanor equal to 1.06.
 40. A method of fracturing a subterranean formationwhich comprising: (a) pumping into the wellbore penetrating thesubterranean formation a gaseous pad fluid at a pressure sufficient toinitiate a hydraulic fracture in the formation; and (b) optionally,mixing a viscosified aqueous fluid into the gaseous pad fluid at a ratioof less than 10 percent by volume of the gaseous pad fluid; and (c)pumping a mixture of a gaseous fluid and a slurry of anultra-lightweight (ULW) proppant in an aqueous fluid into the initiatedfracture, said mixture comprised of at least 90 percent by volume ofgaseous fluid.
 41. The method of claim 40, wherein the amount of ULWproppant placed in the hydraulic fracture is sufficient to create apartial monolayer.
 42. A method of stimulating production ofhydrocarbons in an oil or gas well by creating a partial monolayer ofproppant in the formation, the method comprising: injectingsimultaneously into a wellbore penetrating the subterranean formation aproppant stage which comprises: (1) a gaseous fluid; and (2) an ultralightweight (ULW) proppant suspended in a viscosified aqueous fluid;wherein the gaseous fluid constitutes at least about 90 volume percentof the combination of gaseous fluid and aqueous fluid in the proppantstage; and further wherein the viscosified aqueous fluid contains atleast one viscoelastic surfactant.